The .alpha.,.beta.-unsaturated carboxylic acids and esters have a variety of applications in industries as intermediates in optically active anti-inflammatory drugs, monomers for polymer synthesis, finechemicals etc.
The prior art describes improved process as catalyst systems for employment in improved processes for the preparation of .alpha.,.beta.-unsaturated carboxylic acids and esters. The best known of such catalysts are homogeneous palladium catalysts. Zagarian and Alper, Organometallics 1993,12,712-724 disclosed palladium catalyst hydrocarboxylation of alkynes with formic acid. The catalyst system used in said improved process contained a palladium complex such as palladium acetate, mono as well as diphosphine ligands and formic acid. Even though the improved process required only mild reaction conditions, the conversion rates and product selectivity were low.
U.S. Pat. Nos. 5,166,116 and 5,177,253 describe improved processes for the hydrocarbonylation of alkynes employing a catalyst system consisting of a group VIII metal cation, a source of organic diphosphine having at least one of the phosphorous atoms substituted by an aromatic substituent containing an imino nitrogen atom and a source of an anion. These improved processes give high conversions to a .alpha.,.beta.-unsaturated carboxylic acid esters and good selectivity to iso products, but need severe reaction conditions like a carbon monoxide pressure of 60 atm and use of excess ligands and acid promoters. Another disadvantage of this catalyst system, is the complexity involved in the synthesis of the ligands used, which requires a multistep improved process which requires drastic reaction conditions and is required to be handled strictly under inert atmosphere. Kushino et. al. J. Mol Cat., 89, 1994, 151-158 disclosed the use of a catalyst system comprising palladium bisdibenzilidine complex, triphenyl phosphine and para toluenesulphonic acid for the hydroesterification of alkynes under mild conditions. But their reaction rates and product selectivity were also poor.
Later, A. Scrivanti and U. Matteoli, Tet, lett., 36, 1995, 9015-9018 carried out the hydrocarbonylation of phenyl acetylene and 6-methoxy-2-naphthyl ethyne to corresponding .alpha.,.beta.-unsaturated carboxylic acids using the same catalyst system in the U.S. Pat. Nos. 5,166,116 and 5,177,253. This improved process gives good rates and selectivity to the 2-substituted .alpha.,.beta.-unsaturated carboxylic acids but uses excess ligands and promoters and again the complexities involved in the synthesis of the ligand used are an added disadvantage.
Thus, most of these catalyst systems have several disadvantages in their employment for the carbonylation of alkynes. These disadvantages include the requirement of severe conditions, use of excess ligands and promoters, complexity in ligand synthesis and very low conversion and selectivity. In general, various catalyst systems used for the hydrocarbonylation of alkynes contain a palladium source, a phosphine ligand and an acid promoter.
The applicants have observed during the course of their studies that the use of a palladium source along with a semilabile anionic ligand which is a chelating organic compound containing a N donor and an O group, a monodenate phosphorous ligand and a protonic acid provides an improved catalyst system for the hydrocarbonylation of acetylenically unsaturated compounds to .alpha.,.beta.-unsaturated carboxylic acids and esters. The use of such a catalyst gives high yield and selectivity under normal pressure of carbon monoxide.